Undertrimmer mechanism for sewing machines

ABSTRACT

A trimming mechanism for a sewing machine for severing the marginal edge of the lower ply of material being seamed. Oscillatory movement is imparted to the trimming blade by a series of arms driven off an eccentric on the sewing machine bed shaft. An operator-controlled cam member is operatively connected through its follower to mechanism which changes the relative position of the arms to vary the stroke of the trimming blade and also change its vertical elevation so that the blade at the bottom of its cutting stroke is at the same elevation for any stroke selected.

United States Patent [72] Inventors Erich M. Willenbacher Karlsruhe;Ulrich Schmedtkord, Badenwuerttemberg; Dieter K. Gabler, Neudorl,Germany 864,447 Oct. 7, 1969 May 1 l, 197 1 The Singer Company 1 NewYork, N.Y.

[21 Appl. No. [22] Filed [45] Patented [73] Assignee [54] UNDERTRIMMERMECHANISM FOR SEWING MACHINES 11 Claims, 14 Drawing Figs.

[52] US. Cl 112/127 [51] Int. (1 D05b 37/02 [50] Field of Search112/127,

[56] References Cited UNITED STATES PATENTS 2,064,598 12/ 1936 Fabian etal. 1l2/l27 2,475,758 12/1949 Seaman l 12/127 Primary Examiner-H.Hampton Hunter Attorneys-Marshall .l. Breen, Chester A. Williams, Jr.and

Robert E. Smith ABSTRACT: A trimming mechanism for a sewing machine forsevering the marginal edge of the lower ply of material being seamed.Oscillatory movement is imparted to the trimming blade by a series ofarms driven off an eccentric on the sewing machine bed shaft. Anoperator-controlled cam member is operatively connected through itsfollower to mechanism which changes the relative position of the arms tovary the stroke of the trimming blade and also change its verticalelevation so that the blade at the bottom of its cutting stroke is atthe same elevation for any stroke selected.

PATENTEUMAH 1|97l 3" 577' 944 sum 1 or 4 INVENTORS Erich M- WillenbacherWITNESS Ulrich Schmadfkord.

Dieter K. Gab/er Z/l I V BY yAiTTORNEY I PATENTED MAY] 1 I97l 3,577,944

SHEEI 3 OF 4 BYWW -V TTORNE Y PATENTEU m1 1 19m SHEET UF 4 Fig.Hd

Fig.l|o- Fig.llb

INVENTORS Erich M. Willanbacher Ulrigh Schmedfkord Dieter K. Gab/er BYQM @w WITNESS ATTORNEY UNDERTRIMMER MECHANISM FOR SEWING MACHINESBACKGROUND OF THE INVENTION This invention relates to trimming mechanismfor sewing machines and more particularly to a trimming mechanism forsevering the lower ply of fabric as it is being seamed at a positionproximate'to the seam line.

Certain operations in the manufacture of textile products requiresimultaneously stitching the seam and trimming the marginal edge of oneply of the stitched material. During later operations performed thereon,the wider edge is folded about the trimmed edge and an additional lineof stitching is applied thereto so as to produce a neat and strong seamin which each of the trimmed edges is concealed. In sewing machinesadapted for these operations it is desirable for the operator to be ableto have the capability to adjust the bite of the trimmer blade forvarious purposes, e.g., for trimming different thicknesses of material,to coordinate the trimmer with the stitch length, etc. For the highestspeed of operation of the machine, however, it is necessary that thetotal stroke of the trimmer be as short as possible under thesecircumstances so as to minimize vibration. The present invention allowsthe operator to adjust the stroke of the trimmer blade whilesimultaneously varying its vertical elevationso that substantially allthe variation in the stroke goes into increasing the bite of the blade.

SUMMARY OF THE INVENTION The primary object of this invention is toprovide an improved trimming mechanism for use in a sewing machine whichis adapted to trim a marginal edge of fabric being sewn simultaneouslywith the stitching thereof.

It is a further object of this invention to provide in a sewing machine,a trimming mechanism in .which the stroke of the trimming blade can beselectively adjusted by the-operator to meet various conditions ofoperation and in which the trimming blade can be stopped completelywhile the machine continues to sew.

A still further object of this invention is the provision of a trimmingdevice adapted for use in a sewing machine in which the verticalelevation of the trimming blade is automatically adjusted when thestroke of the blade is adjusted by the operator so that substantiallyall of the increase in stoke goes into in.- creasing the bite of thetrimming blade, thus minimizing wasted motion of the blade, andminimizing vibration.

These and other objects are achieved by providing cam means selectivelyoperated by the operator to move acontrol shaft to adjust the stroke ofthe trimmer blade to the character of the work being trimmed andsimultaneously to effect the vertical elevation of the trimmer blade.The trimmer blade is driven through a driving lever from an eccentric onthe bed shaft. The driving lever is slidably mounted at one end in acarrier frame. Movement of the control shaft varies the location of thefulcrum of the trimmer blade-to change its vertical elevation and alsovaries the direction of oscillation of the driving lever by changing theangular position of t the carrier frame to thus change the stroke of thetrimmer blade.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of thenature and objects of the invention reference should be had for thefollowing description taken in connection with the accompanyingdrawings1 in which:

FIG. 1 is a perspective view of the trimming mechanism of this inventionpartially in section and shown in the maximum cuttingposition;

FIG. 2 is a cross-sectional view through the bed of a sewing machineincorporating the present invention taken substantially along line 2-2of FIG. 1 and showing a fragmented portion of the standard in elevation;

FIG. 3 is a cross-sectional view through the bed of the sewing machinetaken substantially along line 3-3 of FIG. I;

FIG. 4 is a cross-sectional view taken throughthe bed of the sewingmachine taken substantially along line 4-4 of FIG. I and showing the plydeflector used with the present trimming mechanism;

FIG. 5 is a bottom plan view of the sewing machine with a portion of thefeed mechanism broken away and a portion of the frame in section;

FIG. 6 is a view in bottom plan of the trimmer blade and its supportelements as shown in FIG. 5 but removed therefrom for clarity;

FIG. 7 is an enlarged fragmented top plan view of the throat area of thesewing machine showing the position of the trimmer blade in relationthereto and showing the ply separator in phantom;

FIG. 8 is a view similar to-FIG. 7 but on an even larger. scale and withthe accessory plate partiallyv broken away;

FIG. 9 is a cross-sectional view taken along line 9-9 of FIG. 8 showingthe trimmer blade at the top of its stroke prior to the taking of a cutand further showing the ply separator positioned between the two plys-offabric;

FIG. 10-is a cross-sectional view similar to FIG. 9 taken along line10-10 of FIG. 8 but showing thetrimmer blade in its position subsequentto the cutting of the lower ply of fabric;

FIGS. Ila-11d are end views, partially broken away, showing the positionof the trimmer blade relative to the'throat plate of the sewing machinefor various settings of the operator controlled lever; FIG. Ila beingthe no-cut position, FIG. Ilb showing the trimmer blade at the top andbottom of its stroke for the first cutting position, FIG. 11c showingthe trimmer blade at the top and bottom of its stoke for thesecondcutting position and FIG. 11d. showing the trimmer blade at the top andbottom of its stroke for the maximum cutting positron.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing, the invention isillustrated as applied to a zigzag sewing machine having a bed 10 andincluding a bedplate 11 to theupper surface of which is secured an,acces sory plate Ila and a throat plate 12 provided with the usualopenings to accommodate a feed dog 13; Rising from the bed at one end ofthe, bed is a standard 14, the upper end ofwhich has an overhangingbracket arm (not shown) extending above the bedplate I1. and terminatingin a head at its outer extremity (not shown) as is well known in theart. Slidably joumaled in the head for endwise reciprocation and forzigzag jogging movement is a needle bar 15 which carries at its lowerextremity a needle .16. Needle jogging means of any conventional form isadapted to jog the needle in adirection-longitudinally of the-bed 10.Further joumaled-in the head is a presser bar 17 which carries at itslower end a presser foot 18 cooperating with the feed dog 13 to hold andfeed the work in the usual manner in a direction transversely of thebed. A slotted needle aperture 12a extendinglongitudinally of the bed isprovided in the throat plate 12. Cooperating with the needle in theusual manner for forming lock stitches isa rotary loop taker I9 drivenby shaft20 by means of gearing (not shown) within gear boxes 21 and 22.Driving the gearing within the gear boxes is a rotary bed shaft 23deriving its-motion from a pulley 24' on its right end, as viewed inFIG. 5, which in turn, is driven by a belt 25 from a main. shaft (notshown) in timed relation with the needle bar. The feed dog 13 is givenfeed motion by means of the feed bars. 26, 26a which are connected tothe triangularly shaped feed advance bar 27 driven offthe bed shaft 23by means of feed advance rock arm 28. An eccentric (not shown) on bedshaft 23 imparts motion to an arm 29 which in turn, drives the rock arm28. An eccentric (not shown) on stud shaft 30 imparts feed lift motionto the feed bars. The feed mechanism not forming any part of thisinvention is well known in the art and need not be described any furtherat this time. 1

The trimmer mechanism of this invention will now be describedwith'particular reference to FIGS. 1-5. As best seen in FIG. 1, mountedon the bed shaft 23 is an eccentric 31 and a balance wheel 23a. Aneccentric strap connection 32 having a pitman extension 33 transmitsoscillating motion to a driving lever 34. The driving lever comprisestwo parallel wall sections 35 and 35a joined together by a bottomsection 36 and two braces 37 and 37a. The pitman extension 33 is pinnedbetween the walls 35 and 35a. At either end of the driving lever is aforked portion 38 and 39 between the walls 35 and 35a. Joumaled withinthe fork 38 is a cylindrical slide 40 having an aperture 41therethrough. A pin 42 set in a carrier frame or yolk member 43 isadapted to pass through the aperture 41 in the slide. The carrier frame43 is essentially a boxshaped element having one end open for thepassage therethrough of the driving lever 34. As seen in FIGS. 1 and 5,attached to end walls 44 and 44a of the carrier frame are shafts 45 and46 which are joumaled within the bed of the machine as at 47 and 48.Joumaled at 39a within the fork 39 of the driving lever 34 is a crankarm 49 formed at its free end with a split sleeve portion which issecured by means of screw 51 onto a short rock shaft 52 having a stepportion 53 journaled within the frame of the machine as shown at 54 inFIG. 5. Fixed onto the shaft 53 is the hub of a crank arm 55 whose freeend is pinned at 56 to a lever 57. The lever 57 is'in turn pin connectedat 58 to one arm 59 of a bellcrank 60 fulcrumed at 61 as will be laterdescribed. The other arm 62 of the bellcrank 60 is bent at a right angle63 remote from the pivot 61 and has an upstanding portion 64 thereon. Atrimming element 65 is connected to the portion 64 as by screws 66 and67. A slot 67a in the element 65 allows adjustment of the lateralmovement of the trimming mechanism of the trimming element 65.

Joumaled in the bed plate at the standard end of the machine is a pin68, the top of which has a disc 69 connected thereto by means of a setscrew 70. A lever 71 having an operator control knob 72 is fixed withinthe disc 69. The pin 68 passes through a plate 73 which rests on the bedplate 10. Beneath the bed plate the pin is fixed into a cam element 74and locked to the hub thereof by a set screw 75. The cam 74 has a camtrack 76 thereon comprising a series of notches 76a, 76b, 76c and 76dcorresponding to the stroke of the trimmer selected. The notch 76dcorresponds to the no-cut position or the setting where the trimmerblade does not oscillate. Of course, any number of notches more or lessthan the four shown can be used and is within the scope of thisinvention.

In contact with the cam track is a follower pin 77 integral with afollower arm 78 having a split sleeve 79 at its opposite end thereof.The sleeve passes about a control shaft 80 and is locked thereon bymeans of a screw 81 in such relation that the pin 77 is always incontact with the cam track 76. The control shaft further passes throughthe split sleeve 82 of a crank arm 83, the sleeve being fixedly securedto the control shaft 80 by means of a screw 84. The lower end of thecrank arm 83 is pin connected at 85 to one end of a lever 86 whose freeend is pin-connected at 87 to the carrier member 43 below the shaft 46.A moment arm is thus created between the shaft 46 and the connection 87on the member 43. It is, therefore, clear that movement of the leverknob 72 by the operator will cause the control shaft 80 to turn in agiven direction, causing the carrier frame 43 to change its angularrelationship.

Further secured to the control shaft as by a latch member 88 is a leverelement 89. It is seen in FIG. 6 that the latch member 88 has two cars90 and 91, through which pass a screw 92. A finger 93 at the top of thelatch member is forced into engagement with a step 94 on the leverelement 89 when the screw is tightened into these ears. The bellcrank 60is thus fulcrumed at 61 between fork elements 95 and 95a of the leverelement 89 for pivotal movement relative thereto. A bracket 96 at thebottom of the bed is connected by means, for example, of a bolt 97 to acylinder 98. Within the cylinder 98 a spring (not shown) biases a pin 99against the bottom of the lever element 89, so as to maintain the sameupwardly. Between the split sleeve 82 and the lever element 89 thecontrol shaft passes through and is concentric with the rock shaft 52and acts to further journal the rock shaft for oscillatory movement.

A spring 100 secured as by a pin 101 to the bed of the machine at oneend, engages a pin 101a on the carrier frame 43 so as to bias thecarrier frame towards its maximum inclination as shown in FIG. 1. Thisin turn, by means of lever 86 and crank arm 83, tends to keep thefollower pin 77 against the cam track 76. At the standard end of thebed, a bracket 102 is secured beneath the bedplate to a bed by a screw103. A slot 104 in the bracket allows lateral shifting of the bracketrelative to the bed. An upstanding portion 105 of the bracket receivesthe end of the control shaft 80 within an aperture therein. For purposeslater described, a spring 106, between the portion 105 and the splitsleeve 79 biases the control shaft and the elements secured thereto tothe left, as viewed in FIG. 5. Bushings 107 and 108 in the bed of themachine and rock shaft 52 rotatably support the control shaft 80 whichextends therethrough.

As can be seen in FIG. 5, the cam track 76 does not extend entirelyabout the cam 74, but terminates at edges 109 and 110. A stop pin 111protruding from the bed of the machine is adapted to extend into thisregion between 109 and 110, clockwise of 109 in FIG. 5, thus limitingthe movement of the cam between these edges. The pin 111 engages edge109 at the maximum cutting position, as shown, and edge at the no-cutposition so that the operator may easily go to either of these extremes.

Attached to a boss on the bedplate 11 as by an adjustable screw 112 is afabric ply separator 113 which, as best seen in FIGS. 9 and 10, acts toseparate the top ply from the lower ply as the latter is being trimmed.As clearly shown in FIG. 8, the ply separator 113 has a cutout portion114 to provide clearance for the trimmer blade during the latters upwardstroke. There is further provided a tapered upper surface 115 and ahooked position 116 on the ply separator so as to allow the same tointervene between the top ply 117 and the bottom ply 118 as close to thestitching point as possible without deflecting the upper ply in suchmanner as to interfere with the sewing operation.

The trimmer element 65 comprises a trimmer blade 119 having awedge-shaped cutting edge 120. The trimming action is accomplished by ascissors-type movement of the cutting edge against a ledger blade 121 asshown in FIGS. 9 and 10. The bias supplied by spring 106 maintain thetrimmer blade 119 against the ledger blade for proper cutting. Themovement of the trimmer blade takes place in a vertical plane whichpasses normal to the fabric being trimmed. This plane is the plane ofthe paper in FIG. 11. The oscillating movement of the bellcrank 60 aboutfulcrum 61 also creates movement of the trimmer blade in a slightlyarcuate path within this vertical plane.

With the present arrangement, as the stroke of the trimmer blade isadjusted by the operator, the elevation of the lever element 89 ischanged, thus changing the location of the fulcrum 61 relative to thethroat plate 12. The center of oscillation of the trimmer blade istherefore varied simultaneously and automatically with the stroke. InFIG. 11b11d, the location of the trimmer blade is shown in solid at thetop of its stroke and is dotted at the bottom of its stroke. It is thusseen that the bottom of the stroke is always at the same level, which isalso the zero stroke position, for any stroke selected. The

- adjustment in stroke, therefore, goes to increase or decrease theeffective cutting stroke or bite of the blade, thus substantiallyeliminating wasted motion of the blade.

In operation when the operator desires to select a particular bite ofthe trimmer blade, he merely moves the knob 72 until the cam follow pin77 engages one of the notches 76a, 76b, or 76c on the cam track 76.There can be indicia on the bedplate of the machine to indicate theselected stroke if desired. The follower arm 78 being fast on controlshaft 80 thus turns this shaft through an angle determined by the notchor stoke selected. Since crank arm 83 and lever element 89 are also faston shaft 80, they too are rotated therewith.

Movement imparted by crank 83 is transmitted through lever 86 to thecarrier frame 43, thus causing the carrier frame and pin 42 to assume apredetermined angular relationship due to the joumaled relationship ofthe shafts 45 and 46 in the frame. Rotary motion of the bed shaft 23 isconverted into oscillatory motion by the eccentric 31, strap 32 andpitman 33. The driving lever 34 is thus always given an oscillatorymovement, but the path of oscillation is variable. When the pin 42 is inthe neutral or vertical position, the slider 40 and hence the lever 34merely idle up and down along pin 42 about the pivotal connection 390with the arm 49, and substantially no horizontal motion is transmittedto the arm 49 to oscillate shaft 52. If the pin 42 was bent at a radiusequal to the length of lever 34,. then no horizontal motion at all wouldbe transmitted to arm 49. However, when the carrier frame 43 and hencethe pin 42 is placed at an angle to the vertical, the slider 40 has ahorizontal component. The driving lever 34 is thus given this componentof motion which in turn oscillates the rock shaft 52 through the crank49, which in turn oscillates bellcrank 60 about fulcrum 61 by way oflever 57. The amplitude of oscillation transmitted to the rock shaft 52and thus to the trimmer blade 119 is therefore controlled by the angularrelationship of the carrier frame 43 as established by the control shaft80.

The angle through which lever element 89 is turned determines theelevational position of fulcrum 61, and thus the center of oscillationof the bellcrank 60 and trimmer blade 119.

When it is desired to sew without trimming, the operator selects notch76d which sets the carrier frame 43 and pin 42 vertically. In thisposition, no horizontal component of motion is transmitted to the lever49 and the blade does not oscillate. The control shaft 80 in thisposition also lowers the blade 119 to the position shown in FIG. 11a.

The timing of the trimmer blade oscillation is such that it moves upwhen the needle is driven upwardly as seen in FIG. 9, and it moves downto sever a marginal edge 122 of the lower ply when the needle is drivendownwardly, as seen in FIG. 10.

We claim:

1. In a sewing machine having a frame, and stitch forminginstrumentalities including a reciprocating needle mounted in said framefor forming a seam at a stitching location, an improved trimmingmechanism including a trimmer blade mounted for cooperation with aledger blade adjacent to said stitching location for selectivelysevering a marginal edge of material being seamed and capable of varyingthe bite of the trimmer blade while the machine is sewing, comprising acontrol shaft rotatably mounted in said frame, operator-controlled meansin operative engagement with the control shaft for selectively turningsaid shaft a controlled amount, means for pivotally mounting saidtrimmer blade for movement with said shaft, oscillatory meansoperatively connected to said pivotable mounting means for oscillatingsaid trimmer blade in timed relation to said needle reciprocation, andmeans interconnectingthe control shaft andsaid oscillatory means forchanging the amplitude of oscillation imparted to said trimmer blade.

2. In a sewing machine as recited in claim 1 including a rotating bedshaft driven in timed relationship to the needle reciprocation, whereinsaid oscillatory means comprises means for converting the rotationalmotion of the bed shaft into oscillatory motion, a driving leverconnected to said motion converting means to be oscillated thereby,means operatively connecting said driving lever to said pivotablemounting means for pivotably oscillating said trimmer blade, and meanson the driving lever for joining the driving lever to saidinterconnecting means.

shaft.

3. In a sewing machine as recited in claim 2 wherein saidinterconnecting means comprises a carrier frame joumaled for pivotalmovement in the sewing machine frame, guide means mounted in saidcarrier frame interconnecting said carrier frame with the drivin leverjoining means for controlling the path of oscillation 0 said dnvrngever, and means mounted on said control shaft operably connected to saidcarrier frame for selectively'pivoting the same when the control shaftis turned to thereby change the angular relationship of the guide means.

4. In a sewing machine as recited in claim 3 wherein the means forconnecting the driving lever to the trimmer blade mounting meanscomprises a rock shaft, first and second crank arms on said rock shaft,the first of said crank arms being pivotably connected to said drivinglever to be selectively oscillated thereby, the second of said crankarms operably connected to said trimmer blade mounting means tooscillate said trimmer blade when said first crank arm is oscillated.

5. In a sewing machine as recited in claim 3 wherein said driving leverjoining means comprises a slide member pivotably mounted on said drivinglever, said slide member including means defining a hole, said guidemeans comprising a pin mounted at each of its ends in the carrier frameand passing through said hole such that said slide member is constrainedto slidably oscillate along said pin, said driving lever beingoscillated along a path determined by the angular relationship of saidpin.

6. In a sewing machine as defined in claim 5 wherein said operatorcontrolled means comprises a cam member pivotally mounted on said sewingmachine frame, a follower member on said control shaft in contact withsaid cam, and operator biased means in engagement with said cam forselectively pivoting said cam to force said follower to turn the controlshaft :1 controlled amount.

7. In a sewing machine as recited in claim 6 wherein the means forconnecting the driving lever to the trimmer blade mounting meanscomprises a rock shaft, first and second crank arms on said rock shaft,the first of said crank arms being pivotably connected to said drivinglever to be selectively oscillated thereby, the second of said crankanns operably connected to said trimmer blade mounting means tooscillate said trimmer blade when said first crank arm is oscillated.

8. In a sewing machine as defined in claim 7 wherein said cam membercomprises a cam track having a plurality of discrete notches, each ofsaid notches corresponding to a different amplitude of oscillation ofsaid trimmer blade, one of said notches corresponding to a zerooscillation of said trimmer blade.

9. In a sewing machine as defined in claim 8 wherein said trimmer blademounting means comprises a lever element on said control shaft, abellcrank lever pivotably mounted on said lever element for oscillatorymovement relative thereto, and means to secure the trimmer blade to onearm of said bellcrank, the other arm of said bellcrank being operablyconnected to the second of said crank arms.

[0. in a sewing machine as defined in claim 9 wherein said rock shaft isconcentric with and joumaled on said control 11. In combination with asewing machine as defined in claim 10, a material ply separator forintervening between the lower ply and an upper ply of material beingseamed together so that the trimmer blade may act on and sever the lowerply only, comprising a member having a cutaway portion for providingclearance for said trimmer blade, and means to mount said separator onthe sewing machine frame proximate to said stitching location in contactwith the underside of said upper ply so as to prevent said upper plyfrom being contacted by said trimmer blade.

1. In a sewing machine having a frame, and stitch forminginstrumentalities including a reciprocating needle mounted in said framefor forming a seam at a stitching location, an improved trimmingmechanism including a trimmer blade mounted for cooperation with aledger blade adjacent to said stitching location for selectivelysevering a marginal edge of material being seamed and capable of varyingthe bite of the trimmer blade while the machine is sewing, comprising acontrol shaft rotatably mounted in said frame, operator-controlled meansin operative engagement with the control shaft for selectively turningsaid shaft a controlled amount, means for pivotally mounting saidtrimmer blade for movement with said shaft, oscillatory meansoperatively connected to said pivotable mounting means for oscillatingsaid trimmer blade in timed relation to said needle reciprocation, andmeans interconnecting the control shaft and said oscillatory means forchanging the amplitude of oscillation imparted to said trimmer blade. 2.In a sewing machine as recited in claim 1 including a rotating bed shaftdriven in timed relationship to the needle reciprocation, wherein saidoscillatory means comprises means for converting the rotational motionof the bed shaft into oscillatory motion, a driving lever connected tosaid motion converting means to be oscillated thereby, means operativelyconnecting said driving lever to said pivotable mounting means forpivotably oscillating said trimmer blade, and means on the driving leverfor joining the driving lever to said interconnecting means.
 3. In asewing machine as recited in claim 2 wherein said interconnecting meanscomprises a carrier frame journaled for pivotal movement in the sewingmachine frame, guide means mounted in said carrier frame interconnectingsaid carrier frame with the driving lever joining means for controllingthe path of oscillation of said driving lever, and means mounted on saidcontrol shaft operably connected to said carrier frame for selectivelypivoting the same when the control shaft is turned to thereby change theangular relationship of the guide means.
 4. In a sewing machine asrecited in claim 3 wherein the means for connecting the driving lever tothe trimmer blade mounting means comprises a rock shaft, first andsecond crank arms on said rock shaft, the first of said crank arms beingpivotably connected to said driving lever to be selectively oscillatedthereby, the second of said crank arms operably connected to saidtrimmer blade mounting means to oscillate said trimmer blade when saidfirst crank arm is oscillated.
 5. In a sewing machine as recited inclaim 3 wherein said driving lever joining means comprises a slidemember pivotably mounted on said driving lever, said slide memberincluding means defining a hole, said guide means comprising a pinmounted at each of its ends in the carrier frame and passing throughsaid hole such that said slide member is constrained to slidablyoscillate along said pin, said driving lever being oscillated along apath determined by the angular relationship of said pin.
 6. In a sewingmachine as defined in claim 5 wherein said operator controlled meanscomprises a cam member pivotally mounted on said sewing machine frame, afollower member on said control shaft in contact with said cam, andoperator biased means in engagement with said cam for selectivelypivoting said cam to force said follower to turn the control shaft acontrolled amount.
 7. In a sewing machine as recited in claim 6 whereinthe means for connecting the driving lever to the trimmer blade mountingmeans comprises a rock shaft, first and second crank arms on said rockshaft, the first of said crank arms being pivotably connected to saiddriving lever to be selectively oscillated thereby, the second of saidcrank arms operably connected to said trimmer blade mounting means tooscillate said trimmer blade when said first crank arm is oscillated. 8.In a sewiNg machine as defined in claim 7 wherein said cam membercomprises a cam track having a plurality of discrete notches, each ofsaid notches corresponding to a different amplitude of oscillation ofsaid trimmer blade, one of said notches corresponding to a zerooscillation of said trimmer blade.
 9. In a sewing machine as defined inclaim 8 wherein said trimmer blade mounting means comprises a leverelement on said control shaft, a bellcrank lever pivotably mounted onsaid lever element for oscillatory movement relative thereto, and meansto secure the trimmer blade to one arm of said bellcrank, the other armof said bellcrank being operably connected to the second of said crankarms.
 10. In a sewing machine as defined in claim 9 wherein said rockshaft is concentric with and journaled on said control shaft.
 11. Incombination with a sewing machine as defined in claim 10, a material plyseparator for intervening between the lower ply and an upper ply ofmaterial being seamed together so that the trimmer blade may act on andsever the lower ply only, comprising a member having a cutaway portionfor providing clearance for said trimmer blade, and means to mount saidseparator on the sewing machine frame proximate to said stitchinglocation in contact with the underside of said upper ply so as toprevent said upper ply from being contacted by said trimmer blade.